[Feat.] build ChekPoint system for the scrapper.

[rajatkb]

In case of a sudden failure and crash, we don't want the process to restart and start scrapping from the beggining.

** REQUIREMENT **
1 . Add method of Database class inside db.py to store check point information
2. Let user implementing plugin decide how to use the checkpointing system.

Note: Database class uses pymongo and contains no data that is modified after creation of object. So it's safe to say it is thread safe.

[agnes-sharan]

Hi, I'd like to work on this issue!

[rajatkb]

@agnes-sharan I have not received any updated about this issue. If you would not be attending to it , please inform me. I will have it reassigned.

[rajatkb]

@agnes-sharan , removing from asignee for the time being. Incase anybody else can attend to it. If later you can pick it, will reassign the issue 💯